docs: def validate_otp(hsm, args):
      """
      Validate an OTP.
      """
      try:
          res = pyhsm.yubikey.validate_otp(hsm, args.otp)
          if args.verbose:
              print "OK counter=%04x low=%04x high=%02x use=%02x" % \
                  (res.use_ctr, res.ts_low, res.ts_high, res.session_ctr)
          return 0
      except pyhsm.exception.YHSM_CommandFailed, e:
          if args.verbose:
              print "%s" % (pyhsm.defines.status2str(e.status))
          # figure out numerical response code
          for r in [pyhsm.defines.YSM_OTP_INVALID, \
                        pyhsm.defines.YSM_OTP_REPLAY, \
                        pyhsm.defines.YSM_ID_NOT_FOUND]:
              if e.status == r:
                  return r - pyhsm.defines.YSM_RESPONSE
          # not found
          return 0xff